<!DOCTYPE html>
<html>
  <head>
    <style>
      .dropdown {
        position: relative;
        display: inline-block;
      }
      .dropdown-content {
        display: none;
        position: absolute;
        background-color: #f9f9f9;
        min-width: 160px;
        box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
        padding: 12px 16px;
        z-index: 1;
      }
      .dropdown:hover .dropdown-content {
        display: block;
      }
    </style>
  </head>
  <body>
    <div class="dropdown">
      <span>下拉菜单</span>
      <div class="dropdown-content">
        <p>Hello World!</p>
      </div>
    </div>
  </body>
</html>
